J Korean Pediatr Soc.
1999 Aug;42(8):1130-1135.
Comparison between Thyroid Function Test and Radiographic Size of Knee Epiphysis in Neonates with Congenital Hypothyroidism
- Affiliations
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- 1Department of Pediatrics, College of Medicine, Soonchunhyang University, Seoul, Korea.
Abstract
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PURPOSE: Biochemical confirmation of congenital hypothyroidism takes about 10 days, which may result in a delay in diagnosis. The delay could be reduced if a faster method of investigation such as knee radiograph is used. The aim of this study is to assess the value of plain radiography of the knee in providing supportive evidence for the diagnosis of congenital hypothyroidism.
METHODS
Neonates with a screening TSH over 20microunit/mL or free T4 under 0.85ng/dL were referred for further investigation during period of 1992-1998. We included 116 patients whose results were all available. Diagnosis was confirmed by measuring serum TSH, T4, free T4 by radioimmunoassay, radioisotope scan and ultrasonography of the thyroid. Radiography of the knee was obtained and ossification center sizes were measured.
RESULTS
Among 116 neonates, 31 were normal and congenital hypothyroisism was confirmed in 85 neonates. There was a statistically significant difference between the controls and the patients in regards to both biochemical data and knee epiphyseal ossification center size. In the congenital hypothyroidism group, there were a significant difference in biochemical data and knee epiphyseal ossification center size according to the diagnosis, and significant correlation between biochemical data and knee ossification center size, especially with serum T4 and combined mean epiphyseal diameter(r=0.56, P<0.01). In the patient group, simple regression equation was made between biochemical data and knee ossification center size. Combined mean epiphyseal diameter(mm) was 0.544 T4+4.161, combined epiphyseal surface area(mm2) was 2.940 T4+14.283. If T4 is below 7 microgram/dL, combined mean epiphyseal diameter is below 8mm and surface area is below 34mm2.
CONCLUSION
In neonates with abnormal thyroid screening, knee radiograph showing a combined mean epiphyseal diameter of 8mm or less and surface area of 34mm2 or less suggests congenital hypothyroidism prior to biochemical confirmation, requiring thyroxine treatment.
